1. Field of the Invention
The invention concerns a conductor protected against electromagnetic interference.
2. Description of the Prior Art
Conductors or cables for transmission of electrical power or electrical signals can carry electromagnetic interference that can damage the equipment (transmitter and/or receiver) to which the cable or conductor is connected.
The interference can be of many different kinds with varying frequencies and amplitudes.
The most meaningful example is lightning which consists in electrical energy of great amplitude and extending over a wide frequency spectrum. Also, the intensification of telecommunications is increasing stray electromagnetic fields. These fields are produced by various sources such as radio and television transmitters, telephone communications or radar transmissions. The interference can also originate from the electrical power distribution network. It may also be in the form of intentional jamming.
Whatever the source of the pollution, the stray fields are often detected by the cables acting as receive antennas.
Various types of protection have routinely been used until now to combat such interference. An outer conductor forming a Faraday cage is commonly employed to protect cables against external radiated interference. Apparatus and equipment is protected against interference carried by a cable or a conductor by means of a filter at the input of the apparatus or equipment, the filter incorporating inductors, capacitors and diodes. The most frequently employed form of lightning protection is a lightning arrester or surge arrester, or a varistor shunting the conductor to be protected. A varistor is a component having an electrical resistance which is greatly reduced if the electric field exceeds a particular threshold; in this case, the interference is shunted to ground.
A cable having a dielectric material with a non-linear characteristic or a threshold characteristic between the core and the outer conductor has also been proposed.
All these protection means or devices are relatively complex, bulky and costly. Moreover, the threshold of the non-linear materials that can be used is generally too high to protect electronic equipment.
The invention remedies these drawbacks.